@media all and (orientation : portrait){
    .video_bg{
        position:fixed;
        z-index: -9999;
        width: 100%;
        background: #469BD4;
        }
}
/*设备横屏时的样式*/
@media all and (orientation : landscape){
    .video_bg{background: #A900B1;
        position: fixed;
        right: 0;
        bottom:0;
        z-index: -9999;
        width: 100%;
        height: 100%;
    }
}

@media only screen and (min-width:320px) and (orientation:portrait){
    html{font-size:50%;}
}
@media only screen and (min-width:360px) and (orientation:portrait){
    html{font-size:62.5%;}
}
@media only screen and (min-width:400px) and (orientation:portrait){
    html{font-size:75%;}
}

@media only screen and (min-width:600px) and (orientation:portrait){
    html{font-size:100%;}
}

@media only screen and (max-width:768px) and (orientation:portrait){
    .wrap{width:45%;}
}
@media only screen and (min-width:480px) and (orientation:landscape){
    html{font-size:50%;}
}
@media only screen and (min-width:580px) and (orientation:landscape){
    html{font-size:53.5%;}
}
@media only screen and (min-width:730px) and (orientation:landscape){
    html{font-size:75%;}
}
@media only screen and (min-width:900px) and (orientation:landscape){
    html{font-size:87.5%;}
}
@media only screen and (min-width:992px){
    html{font-size:100%;}
}